1. Field of the Invention
The present invention relates to wireless protocols and networks, and particularly to a wireless sensor network with energy efficient protocols.
2. Description of the Related Art
To ensure proper operation of a wireless sensor network (WSN), efficient power consumption must be ensured throughout the network. In addition, self-healing ability of the network, cost efficiency and flexible network architecture must also be provisioned to enable seamless operation of the network. Power consumption is the most important design factor for WSNs. Conserving power at each node, eventually reads to the extension of the overall network life. On the hardware front, efficient design of the node could serve as a major factor in deciding the power consumption figures. At the application level, power conservation can be incorporated into the design of the protocols by introducing novel design and implementation procedures that take the energy reserves into account. For example, minimizing the number of collisions or choosing the shortest path to the destination can help save power.
A major part of the power is wasted during transmission and reception of radio packets. Since transmission and reception is inevitable, short distance transmission and simple circuitry for modulation/demodulation can be employed to save power. It is important to know the causes of energy wastage so that appropriate action must be taken to overcome or reduce them. In WSNs energy wastage occurs in three domains, namely, sensing, data processing and communications. However, the losses during communications are considered to be the major factor of the network life. The different causes of energy wastage have been identified and discussed in the following text.
Packet collisions cause nodes to retransmit, which, in turn, results in wastage of the battery power. A collision occurs when multiple nodes transmit at the same time. Since all the nodes share the same channel, collision avoidance must be ensured for proper delivery of packets within the network. The situation becomes even worse when multiple packets start to arrive at a receiving node simultaneously.
Overhearing means that a node starts receiving packets that are not destined for it. In normal operation, a node receives a packet and then starts to parse it. In this process, the node determines the destination address in the packet header and discards it if the receiving node is not the destination of the packet. The time required to complete this process depends on the length of the packet header and also on the location of the destination address in the header.
The main objective of the WSN is to relay information to the sink. Control packets are, however, necessary for establishing and maintaining efficient performance of the system. A large number of control packets decreases the effective data throughput of the network, and also causes an increase in energy dissipation. So there is a tradeoff between the number of control packets that need to be sent and the throughput of the network. Ideally, control packets should be sent when absolutely necessary to ensure that the network is productive with respect to data packets.
The network must have a high level of fault tolerance in order to be of any practical value. In the setup of a WSN, the nodes are scattered so that the sensed parameters reported by individual nodes represent the situation at different physical locations. Usually individual nodes cannot directly communicate with the sink node. In such cases, data must be relayed through intermediate nodes until it reaches the sink. In case of failure of multiple nodes in the network, the data should still reach the sink node by re-routing or variable power adjustment methods. In short, failure of individual nodes should not affect the operation of the network.
WSNs may include hundreds if not thousands of sensor nodes. New nodes may join the network and older nodes may die out without informing the administrator. In such scenarios, the network must be flexible enough to occupy the changes and to accommodate the variable size while maintaining an acceptable level of integrity.
The deployment cost is a very important design factor for sensor networks because of the large number of nodes required, as well as the fact that in most networks the nodes are disposable. The cost includes both the hardware and the software required to monitor the network.
The limited power supply of the nodes makes it inevitable to use energy conservation techniques to design the network that lasts a longer period of time. It is, therefore, important to know the causes of energy wastage so that appropriate action must be taken to overcome or reduce them.
Once the packets collide, the data gets corrupt. Such packets have to be discarded, and retransmissions have to be requested, increasing the energy consumption in the network. Moreover, when the control packets collide, the complete network setup is affected. The delay in packet delivery also increases due to collisions. As an indirect consequence of retransmissions, the effective throughput of the system decreases, since the majority of the time is wasted in retransmissions.
Overhearing wastes valuable energy in reading and receiving packets that are not intended for the desired node. Moreover, until the completion of this process, all the other packets intended for the node are not received, thus increasing the latency in the network and resulting in collisions.
Over-emitting causes high power dissipation and must be avoided by time synchronization schemes or scheduling. Although the losses in idle listening are not severe, they must also be minimized to increase the network lifetime.
Thus, a wireless sensor network with energy efficient protocols solving the aforementioned problems is desired.